Vacuum system of the APS: operation experience and status report

There are 236 vacuum chambers and 23 special insertion device vacuum chambers installed at the Advanced Photon Source storage ring. Each is fabricated from an aluminum extrusion, followed by machining and welding. The standard vacuum chambers have a vertical aperture of 42 mm with a synchrotron radiation extraction channel of 10 mm, while 21 of the insertion device chambers have an 8 mm vertical aperture with an outside dimension of 10 mm, and two insertion device chambers have a 5 min vertical aperture with an outside dimension of 8 mm. The minimum pole gap in the insertion devices is 10.5 mm and 8.5 mm, respectively. The standard vacuum chambers are installed and aligned to /spl plusmn/150 microns, while the insertion device chambers are aligned to /spl plusmn/75 microns. All chambers have distributed NEG strip pumping, with ion pumps and lumped NEG pumps at locations of high gas loads, such as absorbers. During construction, all vacuum chambers were certified for use at 2/spl times/10/sup -10/ Torr. During operation, vacuum with 100 mA beam current is about 3/spl times/10/sup -10/ Torr. Without the beam, the vacuum is in the 10/sup -11/ Torr range. Both chamber types incorporate an antechamber design. The so-called "NEG dust" effect has not been observed. We have over five years of commissioning and operations experience at the APS, without any sign of aging of all the major components. Important design features and operations experience are discussed.